Origins of an Invasion

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Science  02 Aug 2002:
Vol. 297, Issue 5582, pp. 739
DOI: 10.1126/science.297.5582.739c

In the mid-19th century, a marine mollusk, the herbivorous periwinkle Littorina littorea, began to spread rapidly southward along the eastern coast of the United States from Nova Scotia, with pronounced effects on the coastal ecosystem as far south as Delaware. The origins of this invasion have been debated almost ever since, some claiming it as an early example of the now-familiar pattern of accidental introduction by humans from European coasts, others pointing to archaeological and allozyme evidence suggesting a much earlier presence and differentiation from European populations.

Wares et al. now appear to have laid this controversy to rest with an analysis of mitochondrial and nuclear DNA sequences in L. littorea, which shows that the periwinkle has been resident in North American waters for at least 8000 years. The cause of its rapid spread along the New England coast in the 19th century remains enigmatic. However, alteration of the benthic ecosystem by human activity in the form of increased coastal commerce and fishing must remain a prime suspect. —AMS

Ecol. Lett.5, 577 (2002).

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